1. Field of the Invention
The present invention relates to a valve gear to be placed in a piping system, and a coupling mechanism for coupling together the valve stem of the valve and the driving shaft of an actuator.
2. Description of the Related Art
Referring to FIG. 15, a conventional valve gear to be placed in a piping system comprises a valve 1 comprising a valve element 2 and a valve stem 3, and an actuator 4 having a driving shaft 5 for operating the valve element 2. When coupling the valve stem 3 of the valve 1 and the driving shaft 5 of the actuator 4 together, a bracket 10 is interposed between the valve 1 and the actuator 4, and the valve stem 3 and the driving shaft 5 of the actuator 4 are coupled together by a coupling device 20 as shown in FIG. 15, or the valve stem 3 and the driving shaft 5 of the actuator 4 are coupled together by engaging coupling parts formed in the respective free ends of the valve stem 3 and the driving shaft 5 of the actuator 4 without using any coupling device like the coupling device 20.
When coupling together the valve stem 3 and the driving shaft 5 by either of the foregoing methods, the respective axes of the valve stem 3 and the driving shaft 5 must be aligned. When aligning the valve stem 3 and the driving shaft 5 of the foregoing conventional valve gear, the bracket 10 disposed between the valve 1 and the actuator 4 is fastened lightly to the extremity of the valve 1 and the extremity of the body of the actuator 4 with bolts 21 so that the bracket 10 can be moved for positional adjustment, the respective axes of the valve stem 3 and the driving shaft 5 are aligned, and then the bracket 10 is fastened firmly to the valve 1 and the body of the actuator 4 with the bolts 21 as shown in FIG. 15.
When aligning the respective axes of the valve stem 3 and the driving shaft 5, the valve 1 and the actuator 4 are moved vertically, as viewed in FIG. 16, relative to each other for axial positional adjustment so that the upper coupling end of the valve stem 3 is inserted in the lower coupling groove of the driving shaft 5, and then adjusting bolts 22 and 23 are turned as shown in FIG. 17 for the horizontal positional adjustment of the valve stem 3 and the driving shaft 5 relative to each other. The valve stem 3 is shifted to the right, as viewed in FIG. 17, relative to the driving shaft 5 if the adjusting bolt 22 on the left side is screwed in, and the valve stem 3 is shifted to the left, as viewed in FIG. 17, relative to the driving shaft 5 if the adjusting bolt 23 on the right side is screwed in.
The vertical and the horizontal positions of the valve stem 3 and the driving shaft 5 are adjusted carefully with the bracket 10 lightly fastened to the extremity of the valve 1 and the extremity of the body of the actuator 4 with the bolts 21 to align the valve stem 3 and the driving shaft 5, as shown in FIG. 15, FIG. 16 and FIG. 17 and then the bracket 10 is fastened firmly to the valve 1 and the body of the actuator 4 with the bolts 21 after the valve stem 3 and the driving shaft 5 have been aligned.
Thus, the bracket 10 and the coupling device are indispensable to the conventional valve gear, the procurement and manufacture of those components require substantial costs, and the cost of the valve gear increases accordingly.
Furthermore, the operational of aligning the valve stem and the driving shaft of the actuator is complex, takes much time and requires skill.
Still further, the angular position of the valve stem and that of the driving shaft of the actuator must be matched so that the opening of the valve element is proportional to the angular movement of the driving shaft, which enhances the complexity of the aligning operation and requires further skill.